The present invention relates to a magnetron sputtering cathode apparatus provided with an improved magnet assembly, which is capable of manufacturing a homogeneous thin film having a uniform thickness on the surface of a large area substrate while effectively consuming the entirety of a target surface.
In conventional magnetron sputtering cathode apparatuses, various types of cathode structures have been proposed. Among them, the magnetron cathode type is the most widely applied in industrial fabrication. The reason for this is that production is excellent due to a high film deposition rate. Various types of magnetron cathode are known. In particular, a planar magnetron cathode is most frequently used in the industrial field. Particularly, recently, formation of a homogeneous film with uniform thickness on a large substrate area is in demand for manufacturing liquid crystal display devices. For this reason, a system in which a conventional cathode is fixed in place and a substrate is continuously moved to pass in front of the cathode is applied to the magnetron sputtering cathode apparatus. For instance, the magnetron sputtering cathode apparatus shown in Japanese Patent Application Laid-Open No. 60-86272 is a typical example. However, since such an apparatus is composed of a load lock chamber, a heating chamber, a delivery buffering space, a sputtering chamber and the like, the apparatus unavoidably tends to be large. Also, since a region where no etching (erosion) is effected by ion bombardment tends to remain on the target surface, films accumulate on that region. These accumulated films would be peeled off, generating particles, which results in a reduction in production yield. Also, the conventional apparatus has various problems such as low utilization efficiency of the target caused by its non-uniform consumption, and formation of a heterogeneous film of non-uniform thickness through the sputtering process.
To solve the above-noted problems, recently, studies have been made on a magnetron sputtering cathode apparatus in which a substrate and an electrode that faces the substrate are held at a stationary position to broaden the consumption region of the target. Looking at the structure of magnets in the magnetron cathode, a magnetron sputtering cathode apparatus is shown in Japanese Patent Application Laid-Open No. 5-239640, which apparatus is provided with a magnet assembly having a structure where first and second kinds of magnets units having opposite polarity arrangements of N- and S-poles are alternatively disposed adjacent to each another. This apparatus has the following main advantages.
The selection and arrangement of the magnetic poles of a plurality of magnet units are determined so that ion current generation regions are connected to each other, whereby a cyclic locus representative of a path of the drift motion of an electron (drift electron) may be effectively arranged on the target surface. As a result, the adjacent orbits, or cyclic loci, of the drift electrons are hybridized together to form a wide band of drift electron orbit. The target surface may be subjected to considerably wide etching (erosion) by the hybridized wide band of drift electron orbit. Also, the orbits of the drift electrons that are close to and adjacent to each other are hybridized together without repulsion to thereby stably maintain the discharge on the target surface.
As a result, since the erosion region is broadened on the target surface, it is possible to enhance the utilization efficiency of the target and suppress localization of the erosion region. Also, it is possible to enhance uniformity of the thickness of the thin film formed on the substrate and the homogeneity of the film as well as suppress the particles generated due to the unwanted films being accumulated on the region when no etching (erosion) is effected on the target surface.
On the other hand, an example of the use of magnet units having a magnetic polarity mode similar to that of the above-described Japanese Patent Application Laid-Open No. 5-239640 is shown in U.S. Pat. No. 5,196,105. The electrode shown therein includes a single magnet unit in one cathode. Two cathodes of this type are disposed facing each other in a vacuum chamber and a substrate is interposed between the two electrodes for accumulating thin films. Furthermore, a pair of opposing auxiliary electrodes are disposed on an axis that intersects an axis connecting the pair of cathodes. The auxiliary electrodes are provided with two kinds of first and second magnet units whose polarity arrangements of N- and S-poles are opposite each other. The auxiliary units are usually used as anodes. However, in the disclosure of the United States patent, there is a description of the auxiliary electrodes being used as cathodes. However, there is no specific explanation at all in the case where they are used as the cathodes. Accordingly, from the disclosure, it is impossible to understand the advantages and effects thereof.
Among the prior art proposals described above, in particular, the prior art disclosed in Japanese Patent Application Laid-Open No. 5-239640 will be explained in conjunction with FIGS. 7 and 8. According to this disclosure, such an effect that the erosion region is broadened seems to be acceptable. However, the effect is not complete and the prior art has the following disadvantages.
As shown in a cross-section of FIG. 7, the two kinds of first and second magnet units 706 and 707 are arranged such that the polarities of the N-poles and S-poles oppose each other. Each magnet unit has the same dimension. In this case, the polarities of peripheral magnets 703 of the adjacent magnet units are opposite each other, and therefore, drift electron orbits generated by these units attract each other. Each magnet unit is composed of the peripheral magnets 703 and a central magnet 704. Tunnel-like magnetic lines for generating cyclic drift motion of electrons vary so that the strength of the magnetic field at a corresponding position on the surface of a target 705 decreases. As a result, a weak magnetic field portion 708 is generated as shown in FIG. 7. On the other hand, in portions of the peripheral magnets 703 of the outermost portions where the opposite polarity magnet is not located outside thereof, the strength of the magnetic field on the target surface is increased relative to the other portions. The strong magnetic fields 709 are generated as shown in FIG. 7. For this reason, in the magnetron cathode provided with the magnet assembly where a plurality of the above-described units are arranged, etching is concentrated at the portions of the target surface corresponding to the long side portions of the outermost magnet units, resulting in poor utilization efficiency of the target. Also, reflecting this, the film thickness distribution of the thin film on the substrate is non-uniform.
Furthermore, the present inventors have found that the above-described magnetic mode has another problem. FIG. 8 is a plan view of the same magnet units as those shown in FIG. 7. In FIG. 8, the strength of the magnetic field between the adjacent respective units is greater at A-portions 701 of the upper and lower end portions of the magnets than at B-portions 702 of the central portion of the magnets. This is because magnetization of the magnets that is contributable to the magnetic field of the A-portions (i.e. magnetized surface area) is larger at the upper and lower end portions of the magnets. The surface areas of the N-poles and S-poles which are contributable to the magnetic field established over the A-portions 701 are indicated by 711 and 712, respectively. On the other hand, the surface areas of the N-poles and S-poles that are contributable to the magnetic field established over the A-portions 701 in the B-portions 702 are indicated by 713 and 714, respectively. It is understood that the larger their magnetized surface area (711, 712), the higher the magnetic flux density of the magnetic field formed over an area (701), compared with that over an area (715); that is, the strength of the magnetic field increases. Due to the presence of the portions where the strength of the magnetic field is locally intensified, i.e., the A-portions, the etching effect of the target becomes non-uniform, resulting in non-uniformity of the film thickness distribution and reduction of the utilization efficiency of the target.
In the same way, it is apparent that if the electrodes shown in the above-described U.S. Pat. No. 5,196,105, are operated without any modification, the system suffers from the above-described problems.